linux-kernel - [PATCH] sched/fair: Add SMT4 group_smt

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Message-Id: <20230717145823.1531759-1-sshegde@linux.vnet.ibm.com>
Date:   Mon, 17 Jul 2023 20:28:23 +0530
From:   Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>
To:     peterz@...radead.org, tim.c.chen@...ux.intel.com
Cc:     bristot@...hat.com, bsegall@...gle.com, dietmar.eggemann@....com,
        hdanton@...a.com, ionela.voinescu@....com, juri.lelli@...hat.com,
        len.brown@...el.com, linux-kernel@...r.kernel.org, mgorman@...e.de,
        naveen.n.rao@...ux.vnet.ibm.com, rafael.j.wysocki@...el.com,
        ravi.v.shankar@...el.com, ricardo.neri@...el.com,
        rostedt@...dmis.org, srikar@...ux.vnet.ibm.com,
        srinivas.pandruvada@...ux.intel.com, sshegde@...ux.vnet.ibm.com,
        v-songbaohua@...o.com, vincent.guittot@...aro.org,
        vschneid@...hat.com, x86@...nel.org, yangyicong@...ilicon.com,
        yu.c.chen@...el.com
Subject: [PATCH] sched/fair: Add SMT4 group_smt_balance handling

From: Tim Chen <tim.c.chen@...ux.intel.com>

For SMT4, any group with more than 2 tasks will be marked as
group_smt_balance. Retain the behaviour of group_has_spare by marking
the busiest group as the group which has the least number of idle_cpus.

Also, handle rounding effect of adding (ncores_local + ncores_busy)
when the local is fully idle and busy group has more than 2 tasks.
Local group should try to pull at least 1 task in this case.

Originally-by: Tim Chen <tim.c.chen@...ux.intel.com>
Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
Signed-off-by: Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>
---
 kernel/sched/fair.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 932e7b78894a..9502013abe33 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9532,7 +9532,7 @@ static inline long sibling_imbalance(struct lb_env *env,
 	imbalance /= ncores_local + ncores_busiest;

 	/* Take advantage of resource in an empty sched group */
-	if (imbalance == 0 && local->sum_nr_running == 0 &&
+	if (imbalance <= 1 && local->sum_nr_running == 0 &&
 	    busiest->sum_nr_running > 1)
 		imbalance = 2;

@@ -9720,6 +9720,17 @@ static bool update_sd_pick_busiest(struct lb_env *env,
 		break;

 	case group_smt_balance:
+		/* no idle cpus on both groups handled by group_fully_busy below */
+		if (sgs->idle_cpus != 0 || busiest->idle_cpus != 0) {
+			if (sgs->idle_cpus > busiest->idle_cpus)
+				return false;
+			if (sgs->idle_cpus < busiest->idle_cpus)
+				return true;
+			if (sgs->sum_nr_running <= busiest->sum_nr_running)
+				return false;
+		}
+		break;
+
 	case group_fully_busy:
 		/*
 		 * Select the fully busy group with highest avg_load. In
--
2.31.1